The present invention relates to a method for packaging objects by means of sheets of heat-shrink material, and a corresponding packaging machine.
More particularly, the present invention is included in the specific field of operative methods for packaging objects such as boxes or batches of products (e.g. casks, cans, bottles, etc), by means of sheets of heat-shrink material, in which individual sheets are wound in the form of a xe2x80x9csleevexe2x80x9d around corresponding objects to be packaged, in order then to heat-shrink the said sheets onto the corresponding objects, using the so-called phenomenon of xe2x80x9cmemoryxe2x80x9d (xe2x80x9cresilient memoryxe2x80x9d) with which specific plastics materials are provided, in order to consolidate the packaging.
At present, see for example patents U.S. Pat. Nos. 5,203,144, 5,203,146, 5,463,846 and patent application IT-BO98A-000277 (correspond to EP-99,105229.1 and US-98.09/271,773) in the name of the same applicant as the present patent application, in order to package objects with sheets of heat-shrink material (for example by means of shrinkable polyethylenes), firstly, a piece of heat-shrink material in sheet form is wound around an object in the form of a xe2x80x9csleevexe2x80x9d, and subsequently, the object-piece assembly obtained, is conveyed by means of a belt conveyor into and through a tunnel oven of the convection type (e.g. with forced circulation of hot air), or of the irradiation type (e.g. with infra-red lamps), which has an intake door and an output door, such as to heat the piece during passage inside the said tunnel, to a specific temperature, which varies in relation to the type of shrinkable material, such as to weld to one another the head portion to the tail portion of the piece, which overlap one another and are disposed beneath the object, in order then, after output from the tunnel oven, during cooling, to shrink the said piece onto the object, as a result of the above-described phenomenon of xe2x80x9cmemoryxe2x80x9d, and consequently to consolidate the packaging.
This method and the corresponding machines have a series of disadvantages.
A first disadvantage is caused by the fact that an enormous amount of energy is consumed by the said tunnel oven, inside which there must be formed and maintained during operation, forced air circulation at an indicative temperature of approximately 200-250xc2x0, such as to heat the piece of heat-shrink material in sheet form, to an indicative temperature of 110-130xc2x0 C. in acceptable times, i.e. during the period of time which the object-piece assembly takes to travel from upstream to downstream of the tunnel itself.
In addition, in relation to the above-described disadvantage, it must be emphasised that during operation, the intake door and the output door of the tunnel oven open periodically, in order to permit intake and output of the object-piece assemblies, with consequent dispersion of some kilocalories produced, and thus with a relatively large consumption of energy for production of the said dispersed kilocalories.
A second disadvantage is caused by the fact that some of the kilocalories produced are absorbed by the conveyor which transports the object-piece assemblies, with consequent energy consumption for production of new kilocalories designed to compensate for the said absorption.
A third disadvantage is owing to the fact that a further portion of the kilocalories produced is absorbed by the object wrapped, with consequent energy consumption for the production of new calories designed to compensate for the said absorption.
In addition, in relation to the above-described disadvantage, it must be emphasised that these methods and these devices can be used only to package objects and/or products which, without deteriorating and/or being damaged, can undergo the heating which takes place inside this tunnel oven, i.e. in other words, these methods and these devices cannot under any circumstances be used to package objects and/or products which are degradable in heat and/or heat-sensitive, or inflammable products.
The object of the present invention is to eliminate the above-described disadvantages.
The invention, which is characterised by the claims, solves the problem of creating a method for packaging objects by means of sheets of heat-shrink material, which are wrapped in the manner of a sleeve around the objects, and shrunk onto the latter, in which the said method is characterised in that it provides the use of a sheet of heat-shrink material which is heated to a temperature which is at least equivalent to its xe2x80x9cdefrostingxe2x80x9d temperature, in that the said heated sheet is wrapped around an object to be packaged in the manner of a sleeve with a front portion and a rear portion of the said sheet overlapping one another; in that the said front portion is welded to the said rear portion of the sheet; and in that the assembly obtained is allowed to cool until the sheet shrinks onto the object.
In addition, according to one of its variants, the same invention solves the problem of creating a further correlated method for packaging objects by means of sheets of material, which are wrapped in the manner of a sleeve around the objects and shrunk onto the latter, in which the said method is characterised in that it provides the use of a sheet of heat-shrink material heated in a differentiated manner, in which some areas of the sheet are heated at a different temperature from other areas of the same sheet, and in which the arrangement of these areas is selected in relation to the position which the areas themselves assume relative to the object to be packaged, when the said sheet thus heated is wrapped accordingly around the object to be packaged; in that the said sheet of heat-shrink material heated in a differentiated manner is wrapped around the object to be packaged in the form of a sleeve with a front portion and a rear portion of the said sheet overlapping one another; in that the said front portion is welded to the said rear portion of the sheet, and in that the assembly obtained is allowed to cool until different percentages of heat shrinkage are obtained amongst the said areas previously heated in a differentiated manner.
In addition, the same invention also solves the problem of creating a machine for packaging objects by means of sheets of heat-shrink material obtained from a continuous tape of heat-shrink material, which are wrapped in the manner of a sleeve around the objects and shrunk onto the objects themselves, in which the said machine comprises: first conveyor means, which are disposed upstream and can translate and supply the objects longitudinally along a transport plane; second conveyor means, which are disposed downstream and are slightly spaced relative to the said first conveyor means, giving rise to a first aperture between the said first and the said second conveyor means, which can receive the objects presented by the said first conveyor means and translate them longitudinally along a second wrapping plane, which has an intake end and an output end; third conveyor means, which are disposed downstream and slightly spaced relative to the said second conveyor means, giving rise to a second aperture between the said second and the said third conveyor means, which can receive the objects presented by the said second conveyor means, and translate them longitudinally along a transport plane; wrapping means, which are disposed in the vicinity of the said second conveyor means, including suspended wrapping bars, which are oriented transversely relative to the direction of longitudinal advance of the object, and are translated through the said first and the said second aperture, along an orbital path which circumscribes the second conveyor means, and can transport the sheets of packaging material, for wrapping around the objects to be packaged; supply means, which are disposed beneath and aligned in the vicinity of the said first aperture, and can supply a tape of packaging material; cutting means, which are disposed between the supply means and the said first aperture, and can cut the tape of packaging material transversely; and synchronisation means, which can synchronise the said conveyors and the said operative means with one another; in which the said machine is characterised in that it comprises heating means which are disposed upstream from the said wrapping means in order to heat a cold tape of packaging material to a temperature which is at least equivalent to its xe2x80x9cdefrostingxe2x80x9d temperature.
By means of use of the method and the machine, which is the subject of the present invention, the following results are obtained: the tunnel oven is eliminated; and the objects to be packaged are not heated.
The advantages obtained by means of a the present invention consist, substantially, in that there is a reduction of the overall cost of the packaging machine, in that there is an enormous reduction of the energy consumed in order to carry out the packaging, in that a regular shrinkage of the packaging sheet is obtained, and in that even objects and/or products which are heat-sensitive can be packaged with heat-shrink material in sheet form.
In addition, with reference to the variant embodiments of the operative method which is the subject of the present invention, and the variant embodiments of the packaging machine which is also the subject of the present invention, in addition to the above-described results, the result is obtained of heating a sheet of packaging material in a differentiated manner, in which some areas of the said sheet are heated at different temperatures from the others.
The advantages obtained by means of the said variants substantially consist in the fact that it is possible to optimise and pre-select the areas of heat-shrinkage of the sheet, in order to obtain cooled packaging which is heat shrunk only in specific areas and not in other areas, as well as packaging which has different required percentages of heat shrinkage in different specific areas, in which the said areas and the said percentages of heat shrinkage are selected in relation to the type or shape of the object to be packaged.